Utilizing radioimmunoassays for the estimations of gonadal steroids, gonadotropins, melatonin and luteinizing hormone-releasing hormone (LH-RH), we plan to study several aspects of the regulation of hypothalamic LH-RH secretion by testicular steroids and the neuroendocrine factors regulating the circadian rhythms in testicular secretion. Primary emphasis will be placed (1) on the identification of the gonadal steroid, its site of action in the diencephalon, and the nature of steroidal action on hypothalamic LH-RH secretion, and (2) analysis of the interrelationships between the pineal and adrenals on the testicular secretions. Experimental designs encompass hypothalamic deafferentation, adrenalectomy, pinealectomy, electrical stimulation and lesions in the diencephalon and the subcutaneous and intracranial implants of steroids.